Servo motor duty cycle vs. supply voltage
I have a servo motor that I'm controlling with a simple PID controller for a constant frequency square wave with varying duty cycle. My supply voltage is 5.17V with ~1V drop across my low side driver. The controller sits right around 50% duty cycle to keep the servo open to position A. A reference source states that it should take a 14-26% duty cycle to keep it open to position A. What should the supply voltage be, counting again a 1V drop across the driver?
By my calculation, I've applied an effective (time averaged) 2V source.
2/.26 + 1 = 8.7V
2/.14 + 1 = 15.3V
Is this the correct calculation/conclusion that the servo is built to handle a 9-15V supply?